Field of the Invention
The present invention relates to a power generation apparatus that includes an induction generator and a power generation method that uses an induction generator.
Description of the Related Art
Hitherto, various power generation apparatuses using a synchronous generator are known. For example, Japanese Patent Application Laid-Open 2002-155846 discloses a power generation apparatus that includes a water wheel provided in a waterwork piping system, a synchronous generator that is rotationally driven by the water wheel, and a power converter that converts the output of the synchronous generator and supplies the converted output to a system. The synchronous generator that is used in the power generation apparatus is large and expensive due to its complex structure on the ground that a voltage adjuster for causing an excitation current to flow into a secondary winding wire is needed.
Therefore, for example, as disclosed in Japanese Patent Application Laid-Open 2007-28697, there is proposed a power generation apparatus that has a simple structure and low cost. The power generation apparatus includes a water wheel, an induction generator that is rotationally driven by the water wheel, and an inverter that is connected to the induction generator. The induction generator may generate power by obtaining an excitation current from a system power supply or the like. Further, the inverter adjusts a frequency of an alternating current (an excitation current) supplied from the system power supply or the like to the induction generator.
In such a power generation apparatus, when the power generation apparatus is started, that is, the water wheel starts to rotate, the frequency of the excitation current supplied to the induction generator is gradually increased by the inverter in accordance with an increase in the rotation speed of the induction generator. Then, when the rotation speed of the rotor becomes larger than the synchronization speed (the rotation speed of the rotation magnetic field), power (current) is supplied from the induction generator to the system connected to the induction generator.